Project Summary Severed CNS axons fail to regenerate largely because of the reduced intrinsic growth capacity of adult neurons and poor environment for axon extension. The Co-I's Lab finds that the Wnt family molecules and their receptors are upregulated after spinal cord injury (SCI) and mediates regrowth Among adult failure of injured fiber tracts. several Wnt receptors, Ryk is crucial for mediating repulsive axon growth during development and in CNS after injury.Chondroitin sulfate proteoglycans (CSPGs) generated by glial scars strongly suppress axon extension and are major extrinsic molecular targets for treating CNS injury. The PI's group designed small peptides to block functions of CSPG receptors LAR and PTP? by targeting their critical activity domains and demonstrated their high efficiency for promoting axon growth. Blocking each of the two receptors with 3 combined peptides promotes robust regeneration of injured CNS axons. We hypothesize that inhibiting both Wnt and CSPG signals represents a dual approach of enhancing neuronal growth capacity and reducing environmental inhibitory influence at the lesion site. We propose to stimulate robust axon regrowth in adult rodents with transection or contusion SCI by inhibiting Ryk and LAR/PTP? with genetic and pharmacological approaches available in our labs. In Aim 1, we will study synergistic actions of transgenically deleting Ryk plus each of LAR/PTP? receptors on promoting axon regeneration and recovery in mice with SCI. We will determine whether deleting Ryk plus LAR or Ryk plus PTP? receptors acts synergistically to stimulate axon growth and enhance neuronal plasticity in double knockout mice after SCI. In Aim 2, we will determine whether blocking each of Ryk, LAR and PTP? receptors with antibody or selective antagonists pharmacologically promotes axon regeneration and recovery in adult rats with SCI. We will compare effectiveness of the treatments that target individual receptors in promoting regrowth of multiple descending tracts and recovery of locomotor functions after SCI. In Aim 3, we will study whether combination therapies that block two or three receptors yield better axon regrowth and functional recovery in rats with transection or contusion SCI, aiming to identify the optimal therapy for mammals with SCI. Based on the promising results from our pilot studies, we predict that our combined strategies will promote dramatic regeneration of injured axon tracts and recovery of locomotion function in vivo. Our novel strategy of administering deliverable compounds post-injury may facilitate development of a practical combinatorial therapy for CNS lesions.